1. Field of the Invention
The present invention relates to a short-circuit protection circuit, short-circuit protection method and power supply device, and more particularly, to a short-circuit protection circuit, short-circuit protection method and power supply device capable of stopping providing power to an electronic device quickly when short-circuit occurs, to prevent over-current from damaging the electronic device.
2. Description of the Prior Art
In order to ensure stability of power supply, a power supply device for providing power to an electronic device generally includes a short-circuit protection circuit, for quickly stopping providing power to the electronic device when short-circuit occurs, to prevent over-current from damaging the electronic device.
Please refer to FIG. 1, which is a schematic diagram of a conventional power supply device 10. The power supply device 10 provides power to a load 12 (i.e. an electronic device), and includes a power supply 102 and a short-circuit protection circuit 104. The power supply 102 outputs an input voltage Vin, and the short-circuit protection circuit 104 controls connection between the power supply 102 and the load 12. Under a normal situation, the short-circuit protection circuit 104 turns on the connection between the power supply 102 and the load 12, to transfer the input voltage Vin to the load 12. When short-circuit occurs, the short-circuit protection circuit 104 turns off the connection between the power supply 102 and the load 12, to stop outputting the input voltage Vin to the load 12, so as to prevent over-current from damaging the load 12.
Please refer to FIG. 2, which is a schematic diagram of the short-circuit protection circuit 104 in FIG. 1. The short-circuit protection circuit 104 includes a logic operating circuit 202, a shutdown transistor 204 and a driving transistor 206. The logic operating circuit 202 generates a control voltage Vcon2 to the shutdown transistor 204 according to the input voltage Vin and an over-current protection signal OCP, such that the shutdown transistor 204 can generate a control voltage Vcon1 to the driving transistor 206 accordingly. The driving transistor 206 is turned on to transfer the input voltage Vin to the load 12 according to the control voltage Vcon1, and generates a corresponding load current Iload. The shutdown transistor 204 and the driving transistor 206 are N-type metal oxide semiconductor (MOS) transistors. When short-circuit occurs, the logic operating circuit 202 outputs the control voltage Vcon2 with the same level as the input voltage Vin to the shutdown transistor 204 according to the over-current protection signal OCP and the input voltage Vin, such that the shutdown transistor 204 is turned on, so as to pull the control voltage Vcon1 from a level of a driving voltage Vdriver to a ground level (Vcon1=0V), such that the driving transistor 206 is turned off and stops outputting the input voltage Vin to the load 12, to prevent over-current from damaging the load 12 (i.e. electronic device).
However, as shown in FIG. 2, since the input voltage Vin is in practice provided with a system power source Vdd, the input voltage Vin should be the system power source Vdd minus a voltage across a resistor 208 when a total resistance from the system power source Vdd to the input voltage Vin is denoted by the resistor 208. In such a situation, when short-circuit occurs, over-current increases the voltage across the resistor 208, such that the input voltage Vin drops quickly. As a result, when the shutdown transistor 204 should be expected to be turned on according to the control voltage Vcon2 with the same level as that of the input voltage Vin, the control voltage Vcon1 cannot be pulled to ground quickly since the input voltage Vin is small, such that the driving transistor 206 is turned off too late, and thus the over-current damages the load 12.
In the prior art, a size of the shutdown transistor 204 is increased to accelerate pulling the control voltage Vcon1 to a ground level, so as to improve the issue that the driving transistor 206 is turned off too late. Nevertheless, the driving transistor 206 is still turned off too late, such that over-current damages the load 12. Thus, there is a need for improvement.